Myelodysplasia
Myelodysplasia, more formally known as myelodysplastic syndromes (MDS), encompasses a heterogeneous group of clonal hematopoietic stem cell disorders characterized by ineffective hematopoiesis, resulting in peripheral blood cytopenias and morphologic dysplasia in one or more myeloid cell lines. The pathogenesis involves acquired genetic and epigenetic alterations in hematopoietic progenitor cells, leading to impaired differentiation, increased apoptosis, and a propensity for clonal evolution. Over time, this can progress to bone marrow failure and, in a significant proportion of cases, transformation to acute myeloid leukemia (AML). Health impacts are substantial, as patients often present with symptoms related to anemia, infection, or bleeding, and the disease course is marked by chronic transfusion dependence, reduced quality of life, and increased mortality, particularly in higher-risk subtypes.
Refractory Anemia is characterized by anemia unresponsive to standard therapies, with less than 5% myeloblasts in the bone marrow and evidence of dysplasia in erythroid precursors. Patients typically exhibit isolated anemia with minimal or no cytopenias in other lineages.
This subtype is defined by the presence of 15% or more ring sideroblasts among erythroid precursors in the bone marrow, in addition to anemia and less than 5% blasts. These patients frequently have iron-laden mitochondria visible on Prussian blue staining.
RCMD is diagnosed when there is dysplasia in two or more myeloid cell lines, with less than 5% blasts in the marrow and cytopenias affecting at least two blood cell types. Ring sideroblasts may be present, but are not required.
This category is divided into RAEB-1 (5-9% marrow blasts) and RAEB-2 (10-19% marrow blasts), both of which are associated with a higher risk of progression to AML. Patients present with significant cytopenias and increased marrow blasts.
This type is characterized by an isolated deletion of the long arm of chromosome 5, typically presenting with macrocytic anemia, normal or elevated platelet counts, and a relatively favorable prognosis compared to other subtypes.
This group includes cases that do not fit established categories, often due to unusual clinical, morphologic, or cytogenetic features. Diagnosis is based on persistent cytopenias and evidence of clonal hematopoiesis with dysplasia.
Myelodysplastic syndromes are primarily diseases of the elderly, with a median age at diagnosis between 65 and 70 years. The annual incidence in the general population is estimated at 4 to 5 cases per 100,000, rising to over 20 per 100,000 in individuals older than 70. MDS is more common in men than women, and incidence rates are higher in Western countries compared to Asia. Risk factors include prior exposure to chemotherapy or radiation, benzene, and certain inherited genetic syndromes. Approximately one-third of patients with MDS will progress to acute myeloid leukemia, and overall survival varies widely, from several years in lower-risk subtypes to less than one year in higher-risk forms.
Diagnosis of myelodysplastic syndromes is based on a combination of clinical, hematological, morphological, and cytogenetic criteria. Initial evaluation includes a complete blood count with differential, which typically reveals one or more cytopenias. Peripheral blood smear and bone marrow aspirate/biopsy are essential for identifying dysplastic changes in erythroid, granulocytic, and megakaryocytic lineages, as well as quantifying blast percentage. The presence of ring sideroblasts is assessed by Prussian blue staining. Cytogenetic analysis is crucial for detecting chromosomal abnormalities such as del(5q), monosomy 7, or complex karyotypes, which have diagnostic and prognostic implications. Flow cytometry may be utilized to further characterize abnormal cell populations. Diagnostic criteria require persistent cytopenias, evidence of dysplasia in at least 10% of cells in one or more myeloid lineages, and exclusion of other causes of bone marrow failure. The World Health Organization (WHO) classification system is widely used to subtype MDS based on morphologic, cytogenetic, and clinical features.
The therapeutic landscape for myelodysplastic syndromes includes several agents with distinct mechanisms of action. Imetelstat sodium is a telomerase inhibitor that targets malignant hematopoietic stem and progenitor cells, aiming to reduce the proliferation of dysplastic clones. The combination of cedazuridine and decitabine is utilized as an oral hypomethylating regimen, with cedazuridine inhibiting cytidine deaminase to enhance the bioavailability of decitabine, which functions as a DNA methyltransferase inhibitor leading to reactivation of silenced genes and promotion of cellular differentiation. Luspatercept, a recombinant fusion protein, acts as an erythroid maturation agent by binding transforming growth factor-beta superfamily ligands, thereby enhancing late-stage erythropoiesis and reducing transfusion dependency in patients with anemia. Ivosidenib is an oral inhibitor of mutant isocitrate dehydrogenase 1 (IDH1), utilized in MDS patients harboring IDH1 mutations to impede the production of the oncometabolite 2-hydroxyglutarate and restore normal hematopoietic differentiation. Decitabine, also known as 5-Aza-2'-deoxycytidine, is administered intravenously as a hypomethylating agent, facilitating DNA demethylation and reactivation of tumor suppressor genes. Lenalidomide is an immunomodulatory agent particularly effective in patients with MDS and isolated del(5q), exerting anti-proliferative, pro-apoptotic, and immunomodulatory effects. Azacitidine, another hypomethylating agent, is used to treat a broad spectrum of MDS subtypes by incorporating into DNA and RNA, leading to decreased methylation and cytotoxicity in abnormal cells. Darbepoetin alfa, a long-acting erythropoiesis-stimulating agent, is used to manage symptomatic anemia by stimulating red blood cell production in selected patients.
| Structure | Generic Name | CAS Registry Number | Molecular Formula | Molecular Weight |
|---|---|---|---|---|
| imetelstat sodium (Prop INNM; USAN) | 1007380-31-5 | |||
| cedazuridine/decitabine | ||||
| luspatercept (Rec INN; USAN); luspatercept-aamt | 1373715-00-4 | |||
 | ivosidenib (Rec INN; USAN) | 1448347-49-6 | C28 H22 Cl F3 N6 O3 | 582.961 |
 | 5-Aza-2'-deoxycytidine; beta-decitabine; decitabine (Rec INN; USAN; BAN); dezocitidine | 2353-33-5 | C8 H12 N4 O4 | 228.205 |
 | lenalidomide (Rec INN; USAN) | 191732-72-6 | C13 H13 N3 O3 | 259.261 |
 | 5-azacitidine; 5-azacytidine; azacitidine (Prop INN; USAN); azacytidine; ladakamycin | 320-67-2 | C8 H12 N4 O5 | 244.205 |
| darbepoetin alfa (Rec INN; USAN) | 209810-58-2 |
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Myelodysplasia
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